The
determination of cholesterol is routinely performed in egg-containing
foods. The aim is to determine the amount of the ingredient whole egg or
egg yolk, as these are valuable components. This determination
according to the Paragraph 64 method involves time-consuming, manual
steps. The CHRONECT Workstation Cholesterol allows the fully automated
determination of the egg content in food.
Comparison with the reference method
The
determination of the egg content with the CHRONECT Workstation
Cholesterol is largely based on the specifications of the official
method. The samples are saponified, extracted and starch-containing
samples are subjected to enzymatic starch hydrolysis. For the automated
approach, the processes were partially adapted. In an extensive
comparison of the automated method with the official approach, good
matches of the results were found for different matrices.
System setup
Basis
of the CHRONECT Workstation Cholesterol is the LC-GC technology of Axel
Semrau in combination with an automated sample preparation. The LC-GC
technology connects an HPLC via a special interface with a GC equipped
with a FID. The coupling is done via an interface consisting of a
control unit and a heatable valve unit.
The temperature of the valve
unit can be varied from room temperature to 150 °C. The temperature
control effectively prevents condensation of the HPLC solvent in the
valve unit and improves the stability of the system significantly. An
integrated flushing of the valve unit with carrier gas prevents tailing
of the solvent and possible carryover.
The HPLC system consists of
a binary pump and a UV detector, which is used to check the HPLC
chromatogram and to verify the correct fractionation. HPLC is used to
separate cholesterol from matrix components. A fraction of the HPLC
containing the cholesterol is then transferred from the LC directly to
the GC. The measurement of cholesterol is performed as in the official
method with a FID.
The control of the whole system is done
user-friendly by the software CHRONOS by Axel Semrau. The XYZ robot
CHRONECT Robotic integrated in the system takes over the sample
preparation steps, which are based on the manual procedure of the
Paragraph 64 method. The sample is saponified automatically. After
neutralization an automated liquid-liquid extraction is performed. This
is followed by automated drying using Na2SO4.
Afterwards the again diluted extract is injected into the LC-GC-FID
system. After the analysis, the HPLC is backwashed. This removes any
remaining matrix and significantly improves the operational reliability
and lifetime of the chromatographic columns.
If samples containing
starch are analyzed, the described automatic procedure is extended by
an enzymatic starch hydrolysis; this is also part of the Paragraph 64
method.
The use of LC-GC technology allows the elimination of a
derivatization step. The obtained peak form of the cholesterol is very
good even without derivatization.
Commissioning
All
CHRONECT Workstations are commissioned in advance. In the course of a
comprehensive Factory Acceptance Test not only the correct technical
function but also the analytical performance is checked. This test run
is repeated after the installation in a Site Acceptance Test during
installation in the customer's laboratory. In this way, the analytical
accuracy is verified and the system is ready for use immediately after
installation.
Application from practice
The CHRONECT
Workstation Cholesterol is a common development of Landeslabor
Berlin-Brandenburg and Axel Semrau. The system received the Application Award from Laborpraxis at analytica virtual 2020.